Windows 3.1
In short: Windows 3.1 is a Microsoft operating system (1992).
In more detail: Windows 3.0 (1990) and 3.1 (1992) made Windows successful: overlapping windows, Program Manager, TrueType fonts.
In Depth
Details
Still runs on MS-DOS. Windows for Workgroups 3.11 brought network functions.
See Windows, Microsoft, operating system.
See also: Windows, Microsoft, Operating System (OS)